package com.leetcode.leetcode3;

import java.time.LocalDate;

/**
 * K 个一组翻转链表
 *
 * @author luhd
 * @date 2023-08-25
 */
public class Practice25 {
    /**
     * 给你链表的头节点 head ，每 k 个节点一组进行翻转，请你返回修改后的链表。
     * k 是一个正整数，它的值小于或等于链表的长度。如果节点总数不是 k 的整数倍，那么请将最后剩余的节点保持原有顺序。
     * 你不能只是单纯的改变节点内部的值，而是需要实际进行节点交换。
     *
     * 输入：head = [1,2,3,4,5], k = 2
     * 输出：[2,1,4,3,5]
     */

    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        long epochDays = today.toEpochDay();
        System.out.println(epochDays);
    }

    public static ListNode reverseKGroup(ListNode head, int k) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;

        ListNode pre = dummy;
        ListNode end = dummy;

        while (end.next != null) {
            for (int i = 0; i < k && end != null; i++) end = end.next;
            if (end == null) break;
            ListNode start = pre.next;
            ListNode next = end.next;
            end.next = null;
            pre.next = reverse(start);
            start.next = next;
            pre = start;

            end = pre;
        }
        return dummy.next;
    }

    private static ListNode reverse(ListNode head) {
        ListNode pre = null;
        ListNode curr = head;
        while (curr != null) {
            ListNode next = curr.next;
            curr.next = pre;
            pre = curr;
            curr = next;
        }
        return pre;
    }

    public static class ListNode {
        int val;
        ListNode next;
        ListNode() {}
        ListNode(int val) { this.val = val; }
        ListNode(int val, ListNode next) { this.val = val; this.next = next; }
    }
}
